Helium gas has the potential to be used in a wide range of manufacturing applications. Metal atomization processes, cold spray forming, cooling, and shield gas applications can all benefit in one way or another from the physical properties of helium (an inert gas with high thermal conductivity and high sonic velocity). The primary drawback, however, is its cost. Most of the aforementioned applications use large quantities of gas. The cost of using helium would be prohibitive without some form of recycle system for the used gas. Helium recycle systems, both with and without an integrated permeable membrane system, are well documented in the literature. These systems can be configured to reclaim and recycle in excess of 95% of the helium used by the process. For many applications this gives the customer greater flexibility in the amount of gas used. For some customers a higher flow rate of gas is preferred, but often not economically feasible due to the cost of gas product. Since the recovery for these systems is high, the associated costs for the helium are lower. Where higher flow rates would benefit the customer's process they now have the option to optimize their operation without the economic limitations present with other gases, or once-through helium systems.
The problem with many of these systems is that they have been designed to operate with a largely steady state system. For the most part the inlet impurity levels to the recycle system can be predicted and incorporated into the design. The customer's usage patterns are mainly steady state as well, with predictable usage rates.
However, when a customer has a transient usage pattern, coupled with varying levels of process impurities in the recycled stream, the system requires a complex control scheme to ensure that the system continues to operate optimally and achieve the high recovery levels needed to make the system economically feasible. Allowing the product supply to fluctuate with customer usage patterns allows for a tighter system design. Capital intensive pieces of the system such as the adsorption vessels, molecular sieve, valve and line sizes, and ballast and surge tank sizes can all be minimized by allowing the system to turn-down in times of low customer draw, and turn-up when demand is high. Moreover, the permeable membrane system can be operated in its most efficient region through the utilization of an intricate control routine. This allows for recoveries in excess of 95% over a broader range of operating parameters.